The present invention provides a versatile support tool for a workpiece which gives precise support and positioning of the workpiece with respect to an operational centerline.
There is a continuing need for a support tool to be used in engaging workpieces having a specified open inner diameter, such as tires, and positioning those workpieces in a maintained level and oriented relationship with an operational centerline. The workpiece support tooling of this invention is intended to be utilized with balancing measurement and correction operations but does not necessarily have to be limited to that use alone.
The workpiece support tool of this invention provides an infinite variety of settings for supporting and centering workpieces of varying sizes and shapes about a known centerline. The versatility of the tool of this invention enables the operator to make radial adjustments and on-the-fly adjustments to the tool sizing to adapt the tool to accept such continually changing workpieces. In the art of balancing, this level of versatility and accuracy was previously unavailable with prior art tools which are normally programmed with a specific workpiece size and shape in mind and, therefore, have a specific "open" setting and a specific "closed" setting for each different workpiece.
Non-rigid workpieces such as tires, when positioned on prior art tools, encountered problems in achieving optimum desired balancing results in a repeatable sequence. Devices such as that shown by Lannen in his two patents (U.S. Pat. Nos. 2,431,125 and 3,158,032) have retention arms that simply expand outwardly until the inner circumference of the workpiece exerts a sufficient counter-force to the expanding mechanism. Such prior art mechanisms do not account for influencing factors such as differing workpiece construction and size. Some flexible workpieces, such as tires, will distort when pressed upon their inner circumference or bead. Thus their variety in construction and size will greatly affect the level of distortion to the workpiece created by the forces of the expanding tool. For instance, a thin-walled high-performance tire will distort in a different manner than a thick-walled heavier tire. This distortion severely impacts the quantitative and qualitative accuracy of the unbalance measurement and subsequent corrective procedures.
Other devices, such as that shown by Rexroat (U.S. Pat. No. 3,203,255) overcome the undesirability of flexing the tire during engagement with the support tool by balancing the tire mounted on a hardened wheel. The device shown in Rexroat expands to engage the interior of a solid wheel and stops expanding when it encounters the immovable force of the inflexible wheel. The expansion of the retaining member further acts to push the tire/wheel combination to a centered position with respect to the balancing machine centerline. Since the tire and wheel assembly rests upon receiving arms there are, as a result, large frictional forces which must be overcome to place the workpiece in an accurate centered position. Further, a balancing operation using the Rexroat device must always account for balancing the-wheel, which is undesirable in a manufacturing setting as the wheel does not always remain with the tire after balancing.
The manner in which a workpiece is loaded onto a balancing machine also greatly affects the ultimate accuracy of the balancing operation. Many prior art tools are designed to specifically open and close to retain a workpiece of a specific style. If the style of the workpiece is altered, these prior art tools are incapable of easily adapting to the change. It has been discovered that a tool that is prepositioned loosely enough to load a workpiece sometimes remains too loose to achieve the desired accurate centering and measuring of unbalance. Concurrently, a tool that is set ideally for centering and measuring unbalance doesn't always allow the workpiece to be properly seated and leveled with respect to the centerline, thus deleteriously affecting the angle and amount of the unbalance measurement. This problem is particularly bothersome when operations include the random applications of differing workpieces to the support tool.
There are two distinct methods for balancing flexible workpieces such as tires: non-rotating without inflation and rotating with inflation. Prior to this invention, the use of rotation with inflation was known to achieve an accuracy in imbalance measurement that was almost twice the accuracy achievable through non-rotation. However, rotating balancing can many times, be undesirable because of time considerations and complications due to the additional mechanisms required to keep the inflation seal. Thus, manufacturers are continually striving to achieve the accuracy and repeatability available from a rotating inflated system with the less complicated non-rotating uninflated system.
One method for determining the accuracy of an unbalance measuring system compares how closely the balancing device can duplicate or repeat an unbalance reading when the same workpiece is measured many times over. The common unit for measuring such "repeatability" is in inch/ounces or gm/cms. This unit reflects the amount of unbalance (ounces) at a measured distance (inches) from the centerline of the workpiece. As a general rule, tire manufacturers currently specify that a balancing machine must have repeatability of 1 inch/ounce for a 25-30 pound tire when using the rotating method and 3 inches/ounces when using the non-rotating method of measurement. However, manufacturers are persistently demanding increased accuracy and repeatability.
An object of the present invention is to provide a workpiece support tool that can be accurately sized to accept any workpiece in a repeatable manner and achieve accurate repeatable unbalance measurements.
Another object of this invention is to provide a workpiece support tool that is able to repeatedly position itself at a preselected location without error.
Another object of this invention is to provide a workpiece support tool adaptable to accepting workpieces of differing styles and weights, at random, and sequencing the size of the tool to repeatably achieve an optimum unbalance measurement for each of the differing styles and weights of the workpiece.
Another object of the invention is to provide a workpiece support tool having an infinite variety of settings and the versatility to continually adjust on-the-fly to accept differing workpieces and provide repeatable and accurate balancing measurements.
Another object of this invention is to provide a workpiece support tool that can variably control the position of its workpiece engagement members and the force with which engagement members support the workpiece for balancing.
Another object of this invention is to provide a workpiece support tool having at least three distinct positions of engagement for any workpiece, regardless of style or size: a position for loading the workpiece onto the tool; a position for retaining the workpiece during a balancing operation; and a position for unloading the workpiece after the balancing operation is completed.
Yet another object of the invention is to provide a workpiece support tool for use with a non-rotating balancing method that is capable of achieving balancing accuracies and repeatability equal to or better than that achievable by a rotating balancing method.